Any idea of how much XP 5th-level sorcerer's familiar is worth? So it is included in the masters CR... But what if the master "wins" and familiar "loses" (in effect, dies)?
Would you award xp if someone's intellgent sward was destroyed but they survived and got away?
A familiar should be treated like that - they do not gain xp, the only "advancement" a familiar gets is the increased benefits fro his master gaining a level.
If the familiar's master dies then they revert back to normal animal instead of a "magical" one.
The rules are fairly straitforward on things being treated as part of anotther creatures CR - again compare a familiar to a summoned creature.
If you absolutely feet you had to award xp then award xp for a "normal" creature not for what they became for being under the sorcerer's influence (it is like being under a super "buff" spell).
A hawk is a CR 1/3.
During a normal encounter a partly is assumed to use about 20-25% of their assets.
A familiar is an "asset" - it cost gp to summon and costs xp when lost.
So in a reverse scenario the party would have a certain amount of assets in the encounter.
What was the level of the part?
Assuming the party was 4 PCs at 5th level
The CR of a hawk would be 1/3 so the award would be 300/3 = 100 divided equally amoung the party members so roughly 25 xp each.
But again the rules lead you to believe that no xp should be awarded for defeating the familiar in and of itself.
That does not mean you can't award xp for other things - like overcoming a challenge. Did the party get past (i.e., overcome) what the challenge was supposed to be? If so then they should be award full xp based on the challenge for the encounter.
Did they accomplish a task or story point?
Etc.. . .